This project will investigate the permeability of tumor tissue to macromolecules and large particles. Many novel cancer therapies rely on high-molecular-weight agents that may fail to penetrate adequately into much of the solid tumor. We hypothesize that the tumor interstitial matrix controls penetration bu such agents, and the interstitial mobility of a range of particles in three different tumor types and use a gel model to determine the pore size of the tumor interstitial matrix. We will use a fluorescence photobleaching technique to quantify the in vivo particle diffusion ate, and fluorescence microscopy to measure the relative penetration volume of particles directly injected into the tumor. This approach will reveal whether the tumor interstitial matrix is penetrable by gene vectors or other novel agents and whether modification of the particle size, charge, and configuration can significantly enhance penetration. We will also test the hypothesis that, among tumor types, the interstitial permeability to large particles varies with fibrillar collagen content and organization. We will compare particle mobility with matrix structure and content in various human tumor xenografts implanted in mice, as well as in biopsies of human tumors. We will further test the hypothesis by measuring particle transport after treatments to modify tumor fibrillar collagen content and assembly: tumors will be treated with collagenase, relaxin, or grown in decorin-null mice. Finally, we will measure particle mobility and matrix structure in the same tumor type implanted at three different sites: skin, brain, and liver as well as in biopsies of primary and metastatic human tumors. These measurements will test the hypothesis that organ microenvironment strongly affects the interstitial matrix development of clinical cancer treatments by showing the extent of tumor penetration that can be achieved by agents such as gene vectors, by identifying the particle properties that promote penetration, and by showing which tumors and sites of tumor growth are most appropriate or inappropriate for treatment with large particles. The project will also demonstrate approaches to modify the "physiological barrier" of the interstitial matrix to improve particle penetration; successful experimental approaches may lead to clinically feasible treatments.